Numerous items of medical, industrial, and scientific equipment require the delivery of high voltages from an external high-voltage source. In order to deliver these high voltages, special high-voltage cables (characterized by, for example, internal electric fields of greater than about 4000 V/mm) have been developed for this purpose. In general, it is desired that the high-voltage cables are characterized by good insulating properties. Also, it is often required that the cables possess sufficient flexibility to sustain bends and turns in the pathway between the high-voltage source and the item of equipment, and also to permit flexing of the cable during operation.
Traditionally, flexible high-voltage cables have employed an internal insulating material that is made of a rubber elastomeric material, such as ethylene-propylene rubber (EPR) or ethylene-propylene-diene monomer (EPDM). These materials provide the cable with good flexibility. One disadvantage of these rubber insulations, however, is that they are difficult and expensive to produce. Manufacturing these rubber insulations generally requires dedicated facilities and expensive rubber-producing equipment. Other alternative materials, such as paper and oil and plastic and oil laminations, are also problematic and expensive to produce.
An alternative, less expensive approach is to use conventional thermoplastic processing techniques and equipment to produce an insulating material from a thermoplastic compound. One disadvantage of this, however, is that conventional thermoplastic insulating material is very stiff relative to a rubber insulator. Thus, conventional thermoplastic insulations are not ideal for flexible high-voltage cable.